A hearing aid operates to amplify sounds for users that are hearing impaired. However, when the gain amplification is greater than the attenuation of feedback sound from receiver to microphone, the hearing aid becomes unstable and can produce unwanted whistling sound. Conventionally, echo cancellation techniques have been used to increase the useable gain before the hearing aid starts to produce the unwanted whistling sound. The amount of the increase in useable gain yielded by echo cancellation, referred to as headroom improvement, depends on the merit of the underlining echo cancellation algorithm, which largely depends on how accurate the echo cancellation processing models the characteristics of the feedback path.
Existing hearing aids that provide good headroom improvement rely on an off-line calibration of the feedback path to produce a relatively accurate model of the feedback path. The off-line calibration requires the hearing aid to be connected to special equipment or a computer, usually installed in the office of hearing aid professional (e.g., audiologist). Unfortunately, with hearing aids, the feedback path can change at a result of change in-ear acoustics (e.g., ear canal size, wax condition, head wears (e.g., hat or scarf), etc.). In such cases, for accurate operation, the user must go back to the hearing aid professional's office to get the hearing aid recalibrated.
Existing hearing aids also require comprehensive adjustments by experienced hearing aid professionals to meet patients' individual hearing needs because each patient may have a unique hearing loss. When experienced professionals are not readily available, it is difficult and/or inconvenient for users to have their hearing aids fitted. The self-adjustment or adjustments by less experienced professionals demand the adjustment system to be extremely simple yet can result in accurate results.
Thus, there is a need for a hearing aid that can characterize the feedback path and cancel feedback echoes all by itself, and a need for a simple yet accurate fitting procedure and system to adjust the hearing aid parameters.